Specific fragments of SV40 DNA will be produced by limit digestion with the restriction endonucleases R and Z of Hemophilus influenzae and Hemophilus aegyptius, the DNA will be resolved by electrophoresis in polyacrylamide gels and the total number of specific fragments produced per SV40 genome quantitated. The specific fragments of SV40 produced by both endonucleases will be ordered into an unambiguous circular array thus providing the basis for a physical map of the SV40 genome. Regions of the SV40 DNA involved in so-called 'early' and 'late' transcription or transcribed in SV40 transformed cells, will be mapped by nucleic acid hybridization experiments. Also the in vitro promoter sites for mammalian RNA polymerases will be located by examining the specific template activity of isolated DNA fragments with the purified enzymes. The restriction enzymes will be used to probe two other important phenomena in the SV40 system; namely, (1) the orientation of the SV40 sequences that are integrated in the different adenovirus-SV40 hybrid virus strains, and hence the origin of these bybrid viruses, and (2) the relative uniqueness of the monkey DNA that is matured into SV40 pseudovirions.